摘要:

In order to understand the processes that regulate cell-specific gene expression in early molluscan development, we studied the expression of tubulin genes in embryos ofPatella vulgata(Gastropoda, Mollusca). Tubulin genes are first expressed at the 32-cell stage, which is also the stage at which the embryonic transcription starts. At this stage expression of tubulin genes is observed exclusively in two cells in each quadrant, the trochoblasts. These cells, after one additional division, will differentiate into ciliated and cleavage arrested cells. Later they will form part of the prototroch, the locomotory organ of the free-swimming trochophore larva. A trochoblast-specific α-tubulin gene was cloned and its 5′ upstream region was fused to thelac-Zreporter gene. After micro-injection into 2-cell stage embryos, the expression of this fusion gene appears to be restricted to the trochoblasts at the right time. Mutagenic analysis showed that two elements located between −108 and −42 were essential for a correct spatiotemporal expression. The first element, which contains a putative recognition site for homeobox proteins, acts negatively, the second one positively. In south-western and gel retardation assays we could show that several nuclear proteins are able to bind to these elements. The molecular mechanisms that regulate trochoblast-specific gene expression appear to be evolutionarily highly conserved. The 5′ region of thePatellatubulin gene is not only cell type specifically activated in embryos of this gastropod, but also in embryos of spirally cleaving species from other taxonomic groups, e.g., in a polyplacophoran, a scaphopod, and an annelid.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672557

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Transcriptional regulators are thought to play a key role in cell fate determination and territorial specification in sea urchin. Our goals are to clone transcription factors for studying embryonic development. One approach has been to use promoter binding and gene transfer technology to investigate the mechanisms of transcriptional activation and repression of the early H2A histone gene. By this analysis we identified a transcriptional activator, the MBF-1, that binds to the modulator element of the H2A gene and enhances the activity of the H2A promoter. However, the enhancer activity of the modulator and its interaction with MBF-1 also occurs at the gastrula stage when the early histone genes are shut off. Therefore, the silencing of the early H2A histone gene at late stages of development requires the inactivation of the modulator function. To search for antimodulator sequence elements, we took advantage of our previous work showing the presence of phased nucleosomes specifically positioned on the 3′-spacer and in the modulator of the repressed H2A gene. Evidence is described indicating that a 3′-spacer DNA fragment cloned between the modulator and the basal promoter behaves as an antimodulator element. However, this element does not confer temporal capability to the modulator in its function, suggesting that other elements have to be involved in the regulation of the early H2A expression. The second approach relied on the cloning of genes controlling development using probes of regulators known to be involved in regional specification, such as the homeobox genes, with the aim to understand their possible role through the study of their temporal and territorial expression and through the analysis of the mechanism of regulation of their expression. We present evidence that PIHbox 12, a homeodomain encoding gene, is transiently expressed during the early/mid cleavage stages. The abundance of the transcripts reach their maximum in embryos at the 64/128-cell stage concomitantly with the segregation of the specified embryonic territories. Expression of PIHbox l2 is drastically reduced in the absence of cell contacts and/or Ca ions, suggesting that this gene is transcriptionally activated by signal transduction mechanisms. Whole mountin situhybridization showed that PIHbox 12 transcripts are asymmetrically distributed along the A-V axis, being spatially localized in the blastomeres of the ectodermal lineage. We suggest that PIHbox l2 might be involved in the initial events that lead to the specification of the ectodermal territories.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672558

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This article describes the mechanisms associated with ectoderm differentiation during sea urchin embryogenesis. Using animal half explants and molecular markers for oral and aboral ectoderm cells, we present evidence that inLytechinus pictus, two signals from underlying vegetal blastomeres are required for normal ectoderm differentiation. One signal induces the expression of aboral ectoderm genes and a second restricts oral ectoderm expression to the oral side of the embryo.Strongylocentrotus purpuratusanimal halves behave somewhat differently thanLytechinus pictusin their ability to express aboral ectoderm-specific genes. In order to determine how ectoderm genes are activated in early development, we have analyzed the transcriptional control region of the aboral ectoderm-specificSpec2agene. This control region confers aboral ectoderm-specific expression onSpec2aby means of an aboral ectoderm/mesenchyme cell-specific enhancer and a mesenchyme cell repressor element. TheSpec2aenhancer contains multiple DNA-binding sites for SpOtx, a homeobox transcription factor related toDrosophilaorthodenticle and mouse Otx1 and Otx2. SpOtx is present throughout development but unexpectedly, at stages before late cleavage is found mainly in the cytoplasm. Between late cleavage and early blastula stages, SpOtx translocates into the nucleus. Overexpressing SpOtx by injecting SpOtx mRNA into living eggs results in a thin epithelial ball with essentially all cells displaying aboral ectoderm properties. We suggest a model whereby overexpression of SpOtx leads to premature nuclear translocation and conversion of all progenitor cells in the embryo to an aboral ectoderm fate. Our results imply that SpOtx plays a major role in the differentiation of aboral ectoderm cells during sea urchin development.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672559

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Dimorphic, and sometimes polymorphic, spermatozoa are a feature of many caenogastropod and some archaeogastropod (s.l.) taxa. The two types of sperm, named euspermatozoa (fertilizing) and paraspermatozoa (non-fertilizing) by Healy and Jamieson (1981), are produced simultaneously in the same testicular acini. Paraspermatozoa develop from spermatogonia which are similar in structure to those producing euspermatozoa. Formation of parasperm from paraspermatocytes proceeds by atypical meiotic divisions. Despite the variability in the structure of parasperm of prosobranchs, the morphological changes which occur during paraspermatogenesis are remarkably similar between taxa. Multiple flagella develop from numerous basal bodies which in turn originate from two parent and their satellite centrioles (procentrioles). In parasperm which loose all the chromatin (apyrene sperm), the nucleus initially fragments into a number of vesicles. The chromatin in the vesicles gradually degenerates, the remaining material being discharged from the cell by exocytosis. In those parasperm in which a proportion of the chromatin is retained, the nucleus gradually decreases in size as the chromatin condenses. Electron-dense bodies (vesicles) which are produced either by granular endoplasmic reticulum or Golgi bodies begin to form in paraspermatocytes. These vesicles gradually increase in size and coalesce to form larger dense glycoprotein blocks which form the bulk of the head region of the parasperm. It is suggested that the material which forms these electron-dense blocks is derived from nuclear degeneration.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672560

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The higher Lepidoptera produce two types of sperm, eupyrene and apyrene. Eupyrene spermatozoa are fertile, while apyrene spermatozoa are anucleate and, therefore, sterile. Meiosis differs between the two developmental lines. One of the most obvious differences is the aberrant organization of the apyrene spindles. They possess fewer microtubules than eupyrene spindles and chromosome segregation is irregular. To determine whether micotubule nucleation is impaired in the aprene spindles, the present fine structure study concentrated on the centrosomes in both spermatocyte types. In addition, the presence of gamma-tubulin, a newly discovered tubulin isoform which is prevalent in centrosomes, was determined by anti-tubulin immunofluorescence. The observations showed that centrosome fine structure and appearance of gamma-tubulin containing polar masses were very similar in eupyrene and apyrene spermatocytes in late prophase I and in more advanced cells with spindle formation completed. In particular, pericentriolar material was present in about equal quantities in both cell types. Thus, the aberrant structure and behaviour of apyrene spindles are probably not caused by deficiencies in the amount of pericentriolar material and gamma-tubulin, a molecule which is crucial for microtubule nucleation.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672561

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Experiments done in this laboratory showed 5-hydroxytryptamine (5-HT) stimulates gonadal maturation in male and female sand fiddler crabs,Uca pugilator, and red swamp crayfish,Procambarus clarkii.This action of 5-HT is indirect, 5-HT apparently stimulating release of the gonad-stimulating hormone (GSH) that is present in the brain and thoracic ganglia. For example, studies with ovarian explants showed 5-HT has no direct effect on the ovary. But, when ovarian explants were incubated with 5-HT and brain or thoracic ganglia, the incubation medium produced greater ovarian maturation than did the medium when ovarian explants were incubated with brain or thoracic ganglia alone, 5-HT presumably enhancing GSH release. In males 5-HT not only induces testicular maturation but also development of the androgenic glands. 5-HT in males, as in females, apparently triggers GSH release; but in males GSH in turn stimulates the androgenic glands which release the androgenic gland hormone, resulting in testicular maturation. In contrast, dopamine (DA) inhibits gonadal maturation in both sexes. Methionine enkephalin, like DA, slows ovarian maturation. Red pigment-concentrating hormone (RPCH), like 5-HT, stimulates ovarian maturation bothin vivoandin vitro, apparently by stimulating GSH release. RPCH does not affect the ovary directly. Calcium appears to act here as a second messenger for RPCH. The implications of these findings for enhancing the culture of crustaceans is discussed.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672562

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In male crustaceans—unlike vertebrates—the endocrine and gametogenic functions are clearly separated into distinct organs, the androgenic gland and the testis, respectively. The androgenic gland is thought to be the exclusive source of hormone responsible for sex-differentiation and sexual characteristics in crustaceans. Information on this unique crustacean organ is revised with respect to its structure, secretion and role in the regulation of the expression of sexual characteristics, and intersexuality. Several decapod models are presented for research on sexual differentation in higher crustaceans.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672563

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The effect of eyestalk ablation on morphogenesis and levels of methyl farnesoate (MF) in the hemolymph were investigated in juvenile females of the spider crabLibinia emarginata.The ablated crabs had significantly increased levels of MF in the hemolymph as early as 7 days post-ablation, which continued to increase during premolt. In the intact controls, MF levels in the hemolymph remained low throughout the intermolt and premolt periods. All ablated animals molted to giant juveniles, while the intact controls molted to the adult form. These results strongly suggest that there is a period of the molt cycle which is sensitive to elevated levels of MF in the hemolymph, and that MF has a juvenilizing effect on morphogenesis inL. emarginataand probably in other crustaceans as well.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672564

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

RH5849 is a benzoyl hydrazine analog which has been reported to mimic several effects of the arthropod steroid hormone ecdysone to which it is chemically totally unrelated. In adult Diptera, ecdysone is the hormone that triggers vitellogenin synthesis. We report here that RH5849, upon oral ingestion, is able to induce vitellogenin synthesis in maleDrosophila, Neobellieria, PhormiaandLucilia.This contrasts to data in the literature which showed that RH5849 could not mimic the pupariation-inducing effect of ecdysone in last instar fly larvae. RH5849 neither exerts a juvenile hormone mimicking effect nor behaves as an anti-juvenile hormone in both the Colorado potato beetle andGalleria.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672565

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Uptake of inosine and guanosine was measured in male germ ceils of the polychaeteNereis virensat different stages of development. In spermatogonia I (spg I) and spermatid stages, total inosine uptake at 12°C and ambient concentrations of 100 μmol/1 was relatively low (10–50 nmol·ml of packed cell volume pcv−l·h−1). A rapid increase (150–300 nmol·ml of pcv-1·h−1) was found during transition from spg I to spg II with a subsequent decline to low values (10–30 nmol·ml of pcv−1·h−1) in spermatocyte and spermatid stages. This transient increase may be related to the proliferative activity of spg I stages leading to spg II stages, which increases the demand of purine precursors for nucleic acid synthesis. Inosine uptake of spermatozoa stages was extremely variable, and high uptake rates (10–300 nmol·ml of pcv−1·h−1) were found in some, but not in all, cases. In all stages the uptake rates for guanosine remained at a lower level (below 75 nmol·ml of pcv−1·h−1), and no clear stage specific pattern was evident except for low values (<10 nmol·ml of pcv−1·h−1) in motile spermatozoa. For both nucleosides, two uptake components were identified: a linear component (measured at medium concentrations up to 300 μmol/l) and a saturable component (app. km: 9–60 μmol/l). The latter was inhibited by iodoacetamide suggesting the presence of an ATP-dependent facilitated transport mechanism. The presence of the two uptake components was related to the stage of gamete development: the saturable uptake component present in early spg I changed to a linear uptake in late spg I. In spg II stages, both uptake components were present while in spermatocytes, only the saturable component was present. Spermatids and early spermatozoa showed only a linear uptake. In the coelomic fluid, guanosine (0.5–20 μmol/l) and inosine (>3 μmol/l) were the main nucleosides; during spg II and spermatocyte stages, inosine reached high concentrations (100–1000 μmol/l).

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672566

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor